1. Field of the Invention
The present invention relates to a method and apparatus for testing the quality of an optical disk medium; and more particularly, to such a method and apparatus having improved accuracy and reliability.
2. Description of Related Art
Optical disks are divided into three categories: (1) reproduction only such as CD and DVD-ROM, (2) write-once such as CD-R and DVD-R, and (3) rewritable such as CD-RW and DVD-RAM.
In spite of their different operating principles and usages, these optical disks have a similar structure such as shown in FIG. 1. As shown, a base substrate 100 includes grooves 110 formed therein which also forms lands 120 between the grooves 110. The side walls of the lands 120 are referred to as wobble because the side walls have alternating convex and concave curvature with respect to the center of the optical disk. When tracking a land or groove the adjacent wobble located closer to the center of the optical disk is referred to as the inner wobble, and the adjacent wobble located further from the center of the optical disk is referred to as the outer wobble.
Besides grooves, some of the above-referenced disks in their non-recorded state have pregrooves. Pregrooves are grooves including pits formed during the manufacture of the optical disk which define the format of the optical disk.
In their non-recorded state, optical disks are referred to as non-recorded optical disks. More specifically, a non-recorded optical disk is a disk that does not include user data such as program data.
With these optical disks conventional quality test methods involved recording signals in the lead-in area or main storage area of the disk, reproducing those test signals, and comparing the test signals to reference signals to determine quality.
Unfortunately, however, these methods cannot be applied to every optical disk manufactured. For instance, once test data is written into a write-once optical disk, that disk loses its value as a commercial good. Accordingly, samples from a plurality of manufactured optical disks are taken and tested according to the above-described methodology.
Besides rendering the sampled disks unusable, these quality testing techniques also prove to be inaccurate and unreliable. Just because the sampled disks may be of sufficient quality does not necessarily mean that the other disks, not sampled, are of sufficiently high quality. Therefore, these tests tend to be inaccurate and unreliable.
These optical disk media also undergo additional mechanical quality tests. For instance, the entire surface of the optical disk is displayed by monitoring the scanning of the optical disk surface with a laser beam using a CCD camera. The surface is then visually checked. Other tests include checking the location of the lead-in and lead-out for the main storage area.